The somatomedin class of polypeptides, a group of insulin-like growth factors, consists of somatomedin A and somatomedin C, non-suppressible insulin-like activity, soluble in acid ethanol and multiplication stimulating activity. These peptides are under partial growth hormone control and may require insulin for their synthesis. Human serum levels have been measured in the past by either bioassay or radioreceptor assay, both of which have many limitations. I propose a new method for the purification of these peptides, using the natural affinity of these hormones for their binding proteins. I plan to develop radioimmunoassays for each, and to measure the serum levels in diabetic patients in a variety of natural and provocative situations. I expect these peptides to play a role in the growth retardation characteristic of poor control of juvenile diabetes and perhaps to be involved in diabetic complications such as diabetic retinopathy.